Real-Time Ray-Casting and Advanced Shading of Discrete Isosurfaces

This paper presents a real-time rendering pipeline for implicit surfaces
defined by a
regular volumetric grid of samples. We use a ray-casting approach on current
graphics
hardware to perform a direct rendering of the isosurface. A two-level
hierarchical
representation of the regular grid is employed to allow object-order and
image-order
empty space skipping and circumvent memory limitations of graphics hardware.
Adaptive
sampling and iterative refinement lead to high-quality ray/surface
intersections. All
shading operations are deferred to image space, making their computational
effort
independent of the size of the input data. A continuous third-order
reconstruction
filter allows on-the-fly evaluation of smooth normals and extrinsic
curvatures at any
point on the surface without interpolating data computed at grid points.
With these
local shape descriptors, it is possible to perform advanced shading using
high-quality
lighting and non-photorealistic effects in real-time.

Hierarchical Penumbra Casting

We present a novel algorithm for rendering physically-based soft shadows in complex scenes. Instead of casting shadow rays, we place both the points to be shaded and the samples of an area light source into separate hierarchies, and compute hierarchically the shadows caused by each occluding triangle. This yields an efficient algorithm with memory requirements independent of the complexity of the scene.

Fast Final Gathering via Reverse Photon Mapping

Vlastimil Havran, Robert Herzog, Hans-Peter Seidel,
MPI Informatik

We present a new algorithm for computing indirect illumination based
on density estimation similarly to photon mapping. We accelerate the
search for final gathering by reorganizing the computation in the
reverse order. We use two trees that organize spatially not only the
position of photons but also the position of final gather rays. The
achieved speedup is algorithmic, the performance improvement takes
advantage of logarithmic complexity of searching in trees. The
algorithm requires almost no user settings unlike many known
acceleration techniques for photon mapping. The image quality is the
same as for traditional photon mapping with final gathering, since the
algorithm does not approximate or interpolate. Optionally, the
algorithm can be combined with other techniques such as density
control and importance sampling. The algorithm creates a coherent
access pattern to the main memory. This further improves on
performance and also allows us to use efficient external data
structures to alleviate the increased memory requirements.

The Occlusion Camera

Chunhui Mei, Voicu Popescu, Elisha Sacks,
Purdue University

We introduce the occlusion camera: a non-pinhole camera with 3D distorted rays.
Some of the rays sample surfaces that are occluded in the reference view,
while the rest sample visible surfaces. The extra samples alleviate disocclusion
errors. The silhouette curves are pushed back, so nearly visible samples
become visible. A single occlusion camera covers the entire silhouette of an
object, whereas many depth images are required to achieve the same effect.
Like regular depth images, occlusion-camera images have a single layer thus
the number of samples they contain is bounded by the image resolution, and
connectivity is defined implicitly. We construct and use occlusion-camera
images in hardware. An occlusion-camera image does not guarantee that all
disocclusion errors are avoided. Objects with complex geometry are rendered
using the union of the samples stored by a planar pinhole camera and an
occlusion camera depth image.